Disturbance Observer-Based Control for Three-Phase Grid-tied Inverter With LCL Filter

This paper presents the design and performance evaluation of disturbance observer-based control for grid-tied inverter with LCL filter. The proposed controller consists of combining state feedback control with disturbance observer. Specifically, the composite controller is developed to ensure stable and accurate regulation of the current injected to the grid despite the variation in the system parameters. Such variations can be compensated by the disturbance observer, while the state feedback control takes on the responsibility to ensure the stability of the closed-loop system. The developed controller is designed in the alpha beta stationary frame with a view to cope with both balanced and unbalanced grid voltages. In such a reference frame, the disturbance observer is established to compensate for sinusoidal disturbance with a view to ensure asymptotic tracking of sinusoidal current reference. This mandates using a disturbance observer that has a resonant property to provide accurate estimate of the sinusoidal disturbance. However, under control saturation, the resonator buildup can cause the transient response to deteriorate by exhibiting a large overshoot. This problem is overcome in this work by considering control saturation in the design process. Simulation tests were conducted to evaluate the performance of the controller under different operating conditions. The obtained results show that the proposed controller is capable of achieving a perfect tracking of sinusoidal reference with a good transient response even during control saturation.